240 ANNUAL OF SCIENTIFIC DISCOVERY. 



effected by an operator, unaided by mechanism. A machine for this 

 purpose was accordingly constructed. Two pigmy mill-stones, each 

 seven inches in diameter, made of cellular horn-stone, known vulgarly 

 as French burr, and resembling those used in grist-mills, were pro- 

 cured and supported in the usual way, one above the other ; excepting 

 that the upper one hangs, by means of a bolt, upon a spiral spring of 

 brass wire, sustained by a cross of iron, resting upon screw nuts, 

 upheld by four iron rods, each inserted at its lower end in a circular 

 plate of cast-iron, so as to be equidistant from each other. The sur- 

 face of the iron plate is turned true, so as to enable it to serve as an air- 

 pump plate. It rests upon four columns, which elevate it from a base- 

 board sufficiently to admit of a pulley-band and wheel to work in a 

 parallel plane below that in which the plate is situated. There is also 

 room for a lever, from which a stirrup hangs as a support for the spin- 

 dle of the pulley, on the apex of which plane, extended upwards 

 through a perforation in the axis of the plate, the lower mill-stone rests. 

 The spindle passes through a stuffing-box, so as to be air-tight the 

 stirrup allowing it to retain its perpendicularity, notwithstanding the 

 curvilinear movement of the lever when employed to raise or lower the 

 stone. 



In order to put the apparatus in operation, the lower stone is made 

 to revolve by means of the pulley, band and wheel ; while, by means 

 of the lever, the stone is so raised as to produce sufficient contact with 

 that suspended above it. Under these circumstances, scintillation and 

 the odor, which is the object of inquiry, resulted. In no way, how- 

 ever, could I produce the chemical effects of ozone upon iodized starch 

 or guaiacam. On directing a jet of hydrogen between the stones, it 

 took fire forthwith ; but I could not, by means of an electrometer, detect 

 any electricity. When the upper stone was removed, and a piece of 

 an old file, of a large size, made to scrape over the surface of the lower 

 stone, a conducting connection between the file and an electrometer 

 was productive of no electrical indication. The plate being ground to 

 fit a large receiver, the stones were in successive experiments made to 

 revolve in vacuo, in hydrogen, and in a vacuity previously replete with 

 gas, without any diminution of the luminous phenomena. These, it 

 seems, from the inflammation of the jet of hydrogen, constitute a simple 

 case of ignition. During the collision of flint with steel, a portion of 

 the metal, being struck off, takes fire, and thus is enabled to convey 

 ignition to tinder or punk. The incapacity of two pieces of quartz to 

 produce fire, in like manner, arises from the incombustibility of the 

 particles struck off from them, which consequently cool before they 

 meet any mass with which they are not in contact at the moment 

 when the ignition supervenes. 



As the burr stones are opaque, the light is much less advantageously 

 seen when they are both employed, than when the upper one is re- 

 placed by a comparatively small mass of transparent quartz. The 

 concentration of the frictional force and the transparency of the mass 

 under which the ignition is effected, make the corruscations very bril- 

 liant in a room otherwise darkened. I have lately been informed that 

 iu English potteries, where flint is employed as an ingredient in the 



